Keysight Technologies RP7900 Series, Operating And Service Manual

Page: 76 / 318

In voltage priority mode, large capacitive loads and high inductance leads have the potential to create
ringing and dynamically unstable voltage at the DUT when undergoing sudden load or voltage
changes. ESR tends to mitigate this by dampening the resonance that occurs between the load
capacitance and lead inductance. Lead resistance contributes to the damping effects of ESR but also
increases voltage drop and power dissipation in the load leads. The
Capacitive Load Boundary graphs
in the Characteristics section have guidelines for minimum required ESR as a function of DUT
capacitance under two sets of load lead conditions. This is a function of the voltage
compensation
mode .
For a DUT which has internal capacitance with insufficient ESR as shown in the Capacitive Load
Boundary graphs, such as film capacitor or ceramic capacitors, additional capacitance and series
resistance can be added in parallel to dampen the effects of ringing, as shown in the following figure.
The additional capacitance should be at least 1 to 4 times the value of C
DUT
and the desired ESR
should be chosen based on the Capacitive Load Boundary plots for C
DUT
. This can be implemented
through either the addition of an explicit capacitor and resistor or an electrolytic capacitor with the
appropriate value of rated ESR. The parallel capacitance and ESR must be able to handle DUT-
specific requirements such as current or voltage ripple. In addition, parallel capacitance will limit the
ability of the RPS to measure fast current edges sourced directly from the DUT, as well as slow down
the voltage programming speed and bandwidth.
Typical external
damping network
Transient Voltage Deviation
The specified voltage transient response to a load current step for the RPS may become degraded
when remote sensing with long load leads, especially with low bypass capacitance at the DUT. This
can be manifested as a poorly dampened ringing or even as a well dampened response with very large
peak deviation. This issue is exaggerated in the case of lower voltage, higher current RPS units. To
mitigate this, parallel capacitance can be added at the terminals of interest to reduce the amplitude of
voltage deviation. It is likely an external parallel damping network, as previously illustrated, would be
needed in place of or in addition to a pure capacitor. Generally, a capacitor with low ESR in parallel
with a capacitor with high ESR allows for good stability, minimized transient response voltage
deviation, as well as good voltage noise filtering.
2 Installing the Instrument
76 Keysight RP7900 Series Operating and Service Guide